Welcome to Mytherian Expanded Realms: Yersinia, Undercity of the Rats. You must have the Mytherian Heroic Fantasy basic set in order to use this Expansion. In place of the Goblin Skull Keeps Adventure, or other Expanded Realm, you can now use Yersinia as the setting for new Adventures, challenges, enemies, and events. Unlike before, you must strike out from a Rendar city into the endless tunnels, sewers and passages that have been built over the centuries under the Rendarian Empire, braving deeper and deeper levels until you reach Yersinia, Undercity of the Rats. There you will encounter 20 all new Board Sections full of pipes, gratings, sewers and many hazards such as flooding and the dreaded burning sluge. Dwelling in Yersinia are also the abominations of Renglur, Master of Insanity: the Rats, Rat-people, the Diseased, and other things beyond your worst imaginings. Muster your courage and good luck. You'll need it.